The new North American Digital Cellular Standard EIA/TIA IS-54 calls for a narrowband digital cellular TDMA system using QPSK modulation to transport a bit rate of 48.6 kb/s in a nominal channel bandwidth of 30 khz.
At this bandwidth, the 900 Mhz digital cellular channel can exhibit frequency selective fading, causing intersymbol interference, which can be remedied by adaptive equalization. The equalization and synchronization tasks in the receiver are complicated by the existence of relatively rapid channel time variations resulting from vehicle motion doppler shifts. Although decision feedback equalizers (DFE) were found to yield the best performance/cost tradeoff in narrowband TDMA cellular channel, known algorithms for directly adapting the equalizer parameters are too slow and do not result in sufficiently accurate estimates of the equalizer parameters. Alternative adaptation algorithms for this type of equalizer were also found to be very signal-processing-intensive and do not have satisfactory tracking capabilities.
There is therefore a need for a method of quickly providing or adapting a decision feedback equalizer with new parameters which will permit correction of frequency selective fading on cellular channels.
There is also a need for a method which provides more accurate estimates of the channel parameters.
Accordingly, it is an object of the present invention to provide a method of quickly and more accurately estimating channel parameters used in adapting an adaptive decision feedback equalizer.
Another object of the present invention is to provide a method of modelling the cellular channel as a superposition of weighted and delayed independent discrete Rayleigh propagation paths.